MANCHESTER, N.H. (AP) — Mitt Romney eagerly pocketed an endorsement from two-time New Hampshire primary winner John McCain on Wednesday and bid to convert a single-digit victory in Iowa into a Republican presidential campaign juggernaut. Unimpressed, Newt Gingrich ridiculed the former Massachusetts governor as a liberal turned moderate now masquerading as a conservative.

Former Pennsylvania Sen. Rick Santorum sought to rally conservatives to his side after coming achingly close to victory in the Iowa caucuses.

"This is a wide-open race still," added former Utah Gov. Jon Huntsman, who skipped the Iowa caucuses in hopes of making his mark in next Tuesday's first-in-the-nation primary.

Romney is the odds-on favorite to win the New Hampshire primary, and the endorsement of McCain, an Arizona senator, made his welcome in the state a warm one. ""The time has arrived for Republicans to choose a presidential nominee, a new standard bearer who has the ability and determination to defeat President Obama," said the 2008 Republican presidential nominee, a man with a demonstrated appeal to the state's independent voters.

Already, the Republican field of challengers was dwindling.

Minnesota Rep. Michele Bachmann ended her campaign after a dreary 5 percent showing in Iowa, the state where she was born.

After suggesting he, too, might withdraw, Texas Gov. Rick Perry decided otherwise. "Here we come South Carolina!!!" he tweeted. That primary is Jan. 21, and will mark the first balloting in the South as well as in a state that is part of the Republican Party's conservative, political base nationally.

Iowa, for months ground zero in the Republican race, yielded an almost impossibly close finish.

Romney emerged with an eight-vote victory over Santorum, whose grass-roots campaigning produced a late surge that fell just shy of victory. Texas Rep. Ron Paul finished third, followed by Gingrich, Perry and Bachmann.

A survey of Iowa caucus-goers highlighted the internal divisions in the GOP as it sets out to find a challenger for Barack Obama in the general election campaign.

Romney, who campaigned as the man best positioned to defeat Obama, was the favorite by far among caucus-goers who said that goal was their priority. Paul was preferred by those who said what mattered most was backing a true conservative. Santorum ran particularly well among those who said they were looking for a candidate with strong moral character.

Paul outpolled his rivals among younger voters and gained an estimated 48 percent share of self-identified independents, a group that traditionally plays a major role in determining the outcome of New Hampshire's primary.

"If you look to bringing new people in, the frustrated young people that Obama had, you have to look at my campaign. I mean that's where the enthusiasm is," he said.

McCain, who did well among those voters in 2000 and 2008, urged his New Hampshire audience to deliver "an overwhelming vote that will catapult this candidate to the White House." As Romney looked on, he said, "The time has arrived for Republicans to choose a presidential nominee, a new standard bearer who has the ability and determination to defeat President Obama."

Before leaving Iowa, Romney made the round of early morning interview programs, sounding at times more like an analyst of a race than a competitor.

"I think there's a real boost coming out of Iowa, not just for me but also of course for Rick Santorum and Ron Paul," he said.

At the same time, he brushed aside suggestions that his share of the vote in Iowa, less than 25 percent, was a sign of weakness.

"Ronald Reagan got 29 percent of the votes here and ultimately he was able to become our nominee," said, referring to the 1980 campaign that put Republicans in the White House.

He had a stiffer response to Gingrich, who refused to extend congratulations in the wake of the Iowa outcome.

"I'm sure he's disappointed in the results last night. But I expect he'll go on and mount a spirited campaign," he said.

Spirited might be an understatement, given the sharp escalation in rhetoric from the former speaker in the final hours in Iowa. His campaign purchased a full-page advertisement in the Union Leader, New Hampshire's largest newspaper, calling Romney a Massachusetts moderate.

Talking with reporters in Concord, N.H., the former speaker described himself as a "conservative leader for the last generation," and depicted Romney as something entirely different.

"In that same time period, Governor Romney was first an independent, then repudiated Reagan-Bush, then voted for Paul Tsongas, the most liberal candidate in the '93 campaign, then ran to the left of Teddy Kennedy and then became a moderate to run for governor in Massachusetts in 2002."

Gingrich accused his rival of including state-funded abortions in the health care legislation he signed into law in Massachusetts and said he had "specifically designated Planned Parenthood as a part of Romney care, appointed liberal judges to placate Democrats and raised taxes on business..."

"I suspect it's going to be a very lively campaign," he added.

Gingrich was briefly the leader in opinion polls in Iowa, before his support eroded under the weight of attack ads by a super PAC run by Romney's allies. Short of funds, the former speaker was unable to respond in kind, and declared he would run only a positive campaign.

Having jettisoned that approach, it is unclear how much money his campaign has left after Iowa, and how willing a separate super PAC set up to support him is to spend.

Personally, Romney was able to remain largely above the fray in Iowa's ad wars, generally running positive commercials while his allies took on Gingrich and other rivals.

Except for appearing at debates, Perry is not expected to compete in New Hampshire, saving his energy and cash for South Carolina.

In bowing out, Bachmann bestowed no endorsement. Nor did she say if she intended to seek re-election to the House from Minnesota.